1. Field of the Invention
The present invention relates generally to printing apparatus, and more particularly, to a high speed matrix-type ballistic impact spring head.
2. Description of the Prior Art
High speed printers have been developed to accomodate the high output speed of information which can be delivered by high speed information handling systems.
Printers employing wire matrix ballistic impact print heads provide multiple hard copies of information at a relatively high speed. These printers are characterized in that for each print cycle, the printer does not print an entire character per impact but instead uses an array of wire styli to print selected combinations of dots serially onto the recording medium so that as the recording medium is moved relative to the printhead, successive print cycles generate alpha-numeric characters or other informational indicia. Printheads of this type typically use a separate electromagnetic actuator for each stylus within the printhead.
Ballistic-type matrix print heads generally comprise a stylus guide assembly, a plurality of electromagnetic structures coupled to the guide assembly, each structure including an inner pole piece, an outer pole piece and a coil wrapped around the inner pole piece. A plurality of armatures are disposed radially about the guide assembly. Each armature is associated with one of the electromagnetic structures to form an electromagnetic actuator for transferring electromechanical energy to a stylus. Each of the armatures has an inner end and an outer end projecting outwardly of the associated outer pole piece. A plurality of styli are respectively associated with the plurality of armatures, each stylus being carried by the guide assembly and having an armature engaging end for engaging the inner end of the associated armature and a printing end for impacting a record medium when the stylus is propelled through the guide assembly by energization of the associated electromagnetic actuator.
Ballistics type matrix print heads usually include one or more armature retainers coupled to the guide assembly for retaining each armature in engagement with its associated outer pole. One known ballistics-type matrix printer, as disclosed in U.S. Pat. No. 3,929,214, incorporated herein by reference, uses an armature retainer comprised of a single unitary connector having a central portion connected to the guide assembly and a plurality of resilient arms extending axially outward from the central portion. Each of the arms engages the outer end of one of the plurality of armatures for biasing the armature into engagement with the associated outer pole, while at the same time applying a moment of force to the armature tending to cause the inner end thereof to rotate about the outer pole toward the central portion of the connector.
It is necessary to maintain engagement between the armature and its associated outer pole piece in order to maintain an appropriate magnetic path for the associated electromagnetic actuator. Further, it is desirable to bias the inner ends of the armatures upwardly toward the center portion of the connector for contact with a shock absorbing member mounted therein. Such biasing is intended to effect a simultaneous mutual alignment of the armatures' inner ends so that all actuated styli will strike a record medium at substantially the same instant of time.
However, the unitary connector type of armature retainer described above has led to some disadvantages and problems. For one, the biasing force tending to hold each armature engaged with its associated outer pole piece and to rotate the armature inner end upwardly relative to such outer pole piece is applied on an individual basis by the associated resilient arm of the unitary connector. Thus, since there is the possibility of distortion in some arms and general non-uniformity of structure and design among the arms as a whole due to the fabrication process, it will be apparent that there may be corresponding non-uniformity of armature travel. Such non-uniformity may, of course, result in some of the actuated styli striking the record medium at different instants of time. No capability exists to adjust or modify individual armature travel with this prior art unitary type connector.
Another problem with the unitary connector type of armature retainer results from the resilient nature and use of plural individual arms. It has been found that these arms tend to break off by persons either assembling the head, mounting it into a matrix printer unit, or operating such printer. More specifically, since the arms are independently movable relative to one another, they can be inadvertently bent and broken off. This is especially true when considering the fact that the armature outer ends extend outwardly of the head as a whole. They can thus get caught and moved upwardly, thereby causing the associated arm to be bent upwardly and thereby either distorted or broken.
Another known ballistics-type printhead, as disclosed in U.S. Pat. No. 4,051,941, incorporated herein by reference, uses an armature retainer which is a relatively rigid disc. The armature biasing forces are applied to the armature's outer ends by a rubber O-ring mounted to a peripheral portion of the disc. This retainer also has the problem of possible distortion or general non-uniformity of structure which could result in non-uniformity of armature travel and, as with the previously discussed retainer, it provides no capability to modify individual armature travel distance to correct for distortion or variations in the retainer or in other printhead piece parts.
These and other problems of the prior art are solved by the present invention. The present invention relates to a novel ballistics matrix printhead design having an improved technique of armature retention which is free of the above-mentioned disadvantages and problems.